In general, it is important that birchbark should be separated from the timber to be chipped, because the quality of the cellulose produced from the chippings is considerably improved if the proportion of birchbark in them can be kept low.
The simplest method employed for the separation of birchbark is the use of gravity alone, whereby loose bark falls through apertures between conveyor rollers. This procedure, however, has the disadvantage that only the very smallest and completely detached pieces of bark can fall through the gaps between the conveyor rollers, whereas large and partially detached pieces are carried along with the timber into the pulp cooking process and cause a deterioration of the quality of the product.
Another prior art device employs combining plates of a predetermined shape between the conveyor rollers. However, these solutions have proved unsatisfactory in practice. Therefore, there exists need for a new and practicable apparatus for this purpose.